The main function of the vascular endothelium is the mediation and control of the transendothelialexchanges of water and solutes (both small and large molecules) between blood plasma and theinterstitial fluid, in short the control of vascular permeability. This function is obviously "vital", being critical for normal growth, maintainance and survival of all the cells from all tissues and organs . While the morphological structures involved in transendothelial exchanges have been identified (i.e. caveolae, endothelial specific organelles such as transendothelial channels, fenestrae, vesiculo-vacuolar organelles as well as intercellular junctions), there is very little to no biochemical evidence on the molecular composition of the structures involved, their biogenesis and regulation. The major goals of this research proposal are to elucidate the role of endothelial caveolae and their associated stomatal diaphragms in the transendothelial transport physiology. The findings will also document a novel aspect of the transendothelial transport namely the possibility and ways of its modulation (in rate and components transported). Besides their impact on the understanding of the normal physiological process of the transendothelial transport, the data could be used further in the study of the pathophysiology of several human diseases such as tumor angiogenesis, atherosclerosis, acute and chronic inflammation (both viral and bacterial infections, transplant rejection, allergic encephalomyelytis, Alzheimer disease) where such modulations have been shown to occur. These studies could also provide novel transport related endothelial specific molecular markers that could be used in designing strategies for drugs and gene targeting to selected microvascular beds. The techniques employed are cell fractionation, biochemical assays, cell free-assays, in-vivo transport studies, genetically modified animal models, cell culture, transfections, light and electron microscopy.